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Class D Switching Power Amplifiers and Power D/A conversion

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Old 3rd December 2009, 06:37 AM   #21
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Reverting to the post-starter's question, I would say that for efficient speakers and most bookshelf speakers, any Class-D amplifier would compare poorly to something like this:

20W Class A Amplifier Full Kit - Volt Electronics

And the price is for everything including the chassis.
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Old 7th January 2010, 09:26 AM   #22
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Originally Posted by Ian Millar View Post
And the price is for everything including the chassis.
Sorry for self-quoting but it probably would not put a 250mV 200KHz potentially tweeter-frying signal into your speakers either!
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Old 7th January 2010, 09:39 AM   #23
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Yes, because the ClassD forum is full of reports of burnt tweeters..
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Old 9th January 2010, 06:28 PM   #24
Javin5 is offline Javin5  Switzerland
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Originally Posted by Ian Millar View Post
Sorry for self-quoting but it probably would not put a 250mV 200KHz potentially tweeter-frying signal into your speakers either!
Are you really claiming that such a small signal would do any damage to the tweeter? At these high frequencies, the tweeter impedance is usually in the range of about 30 Ohm, which limits the tweeter current to about 8 mA, which would generate a miniscule power well below 1 mW on the resistive part of the tweeter impedance. This is completely safe and orders of magnitude below of what is required to damage a tweeter. I suspect that the damages reported are due to some malfunction or improper DIY-mods. You can get any non-class-D amp into oscillation and burn the tweeter as well; sometimes an improper mod is not even required, in some cases it may be suffient to connect expensive, boutique speaker cables with high enough capacitance. In summary, I don't think that it is fair to blame class-D here. I have UcD amps for several years now without any problem. And yes, I did make the above rough calculation before I built them.

Kurt
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Old 9th January 2010, 11:08 PM   #25
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Originally Posted by Javin5 View Post
Are you really claiming that such a small signal would do any damage to the tweeter?
Kurt
Maybe not on its own, but what if it were to beat with certain high frequency input signals (as might be present as an artifact on an SACD for example) and produce higher voltage square waves? I have seen it (with a function-generated sine wave input signal of 100kHz) on a scope to which my own UcD amp was attached.

I really don't know if damage would result. That's why I used the word "potentially", but tweeters are the least robust of the drivers and a Zobel network can always be added across the amplifier outputs (if you really want to drive tweeters with Class-D for some reason) to reduce the magnitude even further. And a Zobel network is a lot cheaper than some silly boutique speaker cable.

Yes other problem amps can oscillate, but Class-D amps must oscillate by design. To my conservative mind, one less oscillation in the audio path can only be a good thing.

I'm not anti-Class-D. I use it for bass in a bi-amp arrangemend with great results.
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Old 10th January 2010, 10:47 AM   #26
jpetek is offline jpetek  Germany
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Hi,

I heard a Kharma MP 350 (Kharma International | Amplifiers | Exquisites | Mono Power Amplifier 350 (MP350)) , the basic I think a Hypex Modul like the UCD400, but with Modifications (I think on the power supply) and a very heavy Cabinet.

Very good sound. Did anybody know how you can tune a UCD400 or 700?

regards

Josef
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Old 10th January 2010, 12:27 PM   #27
Pano is online now Pano  United States
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I've yet to see a burnt tweeter from Class-D. I used to be afraid that it would be a problem, but so far have never seen it.
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Old 10th January 2010, 05:58 PM   #28
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I have UcD amps for several years now without any problem. And yes, I did make the above rough calculation before I built them.

Kurt[/QUOTE]

+1. UcD in every room and UcD for the PC.
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Old 13th January 2010, 03:25 AM   #29
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The test was conducted by a very experienced and unaffiliated technician. It was sufficiently frightening to him that he refused to connect the amp to his speakers. It is therefore sufficiently frightening for me.

He suggested the addition of Zobels (10 Ohm, 100nF) across the amp's outputs if it is to be connected to tweeters (which it isn't but I saw no harm). He said the iron-cored inductor coil on each module was cheap and filtered too little of the carrier frequency. It doesn't matter what you call it. The word "oscillation" is good enough. It just happens to be designed into the thing rather than being caused by a fault condition.

An interesting (and well-informed) article that talks about amplifier output Zobels is here:

Elliott Sound Products - Audio Power Amplifier Design Guidelines

You suggest that Zobels are not robust, but the above article suggests to me that the capacitor short condition is only applicable at very high inaudible frequencies in which case the robustness is determined by the wattage of the resistor. If your Zobels are fragile, maybe you need bigger resistors.

If you like Class-D for tweeters then that's okay. I like Class-A and that's my prerogative and I am free to express it. And I do so without resorting to rudeness, obscure put-downs or rhetorical questions.
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Old 13th January 2010, 03:38 PM   #30
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